This Program Project Grant began 30 years ago when we defined the LDL receptor (LDLR) pathway for control of cholesterol metabolism and showed that defects in LDLR produce Familial Hypercholesterolemia (FH) and its attendant atherosclerosis. After 30 years, our goals have broadened and the participants have increased, but the focus remains the same: to understand the genetic and molecular basis for regulation of lipid metabolism and to use this knowledge to prevent and treat lipid-related diseases, including atherosclerosis, diabetes, and neurologic diseases. During the last grant period, we published 183 papers. These papers report the following major advances: 1) discovery of Insig proteins as central to feedback control of cholesterol and fatty acid synthesis;2) development of new methods to demonstrate direct cholesterol binding to the sterol-sensing protein Scap;3) demonstration that cholesterol 24-hydroxylase mediates cholesterol turnover in adult brain;4) discovery of new roles for LDLR family members in brain development and function (VLDL and apoE2 receptors) and in vascular integrity and atherogenesis (LRP1);5) demonstration that cholesterol-rich caveolae regulate growth factor receptor tyrosine kinases;6) identification of 4 new genes and their causative roles in 3 human genetic diseases: sitosterolemia (mutations in ABCG5 and ABCG8);autosomal recessive FH (adaptor protein ARH);and selective 25-hydroxyvitamin D deficiency (vitamin D 25-hydroxylase);7) use of knockout mice to show that PCSK9 is a major regulator of LDLR protein levels in liver;and 8) development of the nonsynonymous codon approach to find causative genes in quantitative traits (e.g., loss-of-function mutations in PCSK9 lower LDL by 35% in 2% of African-Americans). We now apply for a 5-year renewal (Years 31-35) to further study these and related phenomena through an integrated and multidisciplinary approach. We propose to learn more about already-known molecules and discover new ones that regulate 3 processes: 1) cholesterol and fatty acid metabolism (SREBPs, Scap, Insigs, MOBP, HMG CoA reductase, PCSK9, LDLR, NPC1L1, ABCG5/G8, putative new insulin-sensitizing factor);2) oxysterol and bile acid metabolism (cholesterol 24-hydroxylase, new sterol hydroxylases);and 3) caveolae membrane function, lipoprotein receptors, and cell signaling (caveolin-1, LRP1, LRP1B, PDGRF(, EGFR). We will continue to study these processes at all possible levels - the molecular (i.e., gene, mRNA, protein), the intact cell, the whole animal, and the human patient. In conducting these studies, we will use multiple techniques - biochemistry, molecular biology, genetics, cell biology, gene-manipulated mice, animal physiology, clinical genetics, and human genomics. This interdisciplinary approach is possible only through support of this Program Project Grant.